In a typical wireless communication system such as a cellular radio frequency (RF) radiotelephone system, a base station having a controller, a plurality of transmitters and receivers and one or more antennae, communicates with a switching center and with a mobile communication unit, or mobile station, operating within an area served by the base station.
Multiple access wireless communication between the base station and the mobile station occurs via RF channels which provide paths over which communication signals such as voice, data and video are transmitted. Base-to-mobile station communications are said to occur on a forward- or down-link channel, while mobile-to-base station communications are referred to as being on a reverse- or up-link channel. Time division multiple access (TDMA) is one example of a well-known channelization technique. A communication system using TDMA channelization is described in detail in Recommendation documents for the Global System for Mobile Communications (GSM), as well as in other standards documents such as Interim Standard (IS) 54 and IS-136, promulgated by the Telecommunications Industry Association, Washington, D.C. GSM recommendation documents, IS-54 and IS-136 describe the services and/or features of a TDMA system to users of such a system as well as performance and equipment specifications for network and portable radiotelephones operating within such a system, and are each incorporated herein by reference.
As shown in FIG. 1, external path loss 20, caused by signal fading, among other things, contributes to total path loss 16. In addition, a down-link internal path loss 10, that is, the difference between actual power radiated from base station transmitter 12 and power radiated from antenna 14, contributes to the total path loss 16 seen by mobile communication unit 18. Down-link internal path loss 10 may be caused, among other things, by normal operation RF cabling, combiners, power amplifiers and other devices, as well as by defects in such devices.
Down-link internal path loss 10 is typically measured by hardware (not shown), such as a test mobile station, located at a fixed position near base station transmitter 12. Such hardware is generally expensive to implement and maintain throughout a multi-cellular communication system having many base stations.
There is therefore a need for a method for determining a transmit power of a base station, and thus the down-link internal path loss associated with the base station, without using dedicated test hardware.